Hitherto, there have been various proposals for an electrophotographic image-forming member having a photoconductive layer composed of an amorphous silicon carbide. For example, in U.S. Pat. No. 4,539,283, there is disclosed a photoconductive member having an amorphous silicon layer containing carbon atoms in a distribution uneven in the layer thickness direction. In U.S. Pat. No. 4,677,044, there is disclosed a photosensitive member having a charge transporting layer comprised of an amorphous silicon carbide, a charge generating layer comprised of an amorphous silicon and a surface modifying layer comprised of an amorphous silicon carbide. And, in U.S. Pat. No. 4,673,629, there is disclosed a photoreceptor having a charge transport layer comprised of an amorphous silicon carbide, a charge generating layer comprised of an amorphous silicon, a surface modifying layer comprised of an amorphous silicon carbide and an interlayer comprised of an amorphous silicon carbide.
It is known that these known amorphous silicon carbide films can be prepared in accordance with a conventional high frequency plasma chemical vapor deposition process (RF PCVD process in short) in the same manner as in the case of preparing a hydrogenated amorphous silicon film in accordance with said RF-PCVD process.
In comparison with the known hydrogenated amorphous silicon films, any of those known amorphous silicon carbide films is inferior with the viewpoint that it is more or less accompanied with not only defects due to hydrogen atoms but also other defects due to double bonds of carbon atoms. Further, for those known silicon carbide films, although they have been evaluated as exhibiting a high dark resistance, they are still problematic in that carbon atoms incorporated therein are apt to cause an increase in the tail state in the conduction bond side depending upon the situation of carbon atoms to be incorporated, which results in decreasing the mobility of an electron. In this respect, there is a limit for those known amorphous silicon carbide films to be used as a constituent layer for an electrophotographic image-forming member.
That is, as for known electrophotographic image-forming members having a photoconductive layer composed of a known amorphous silicon carbide, their electrophotographic characteristics have been considered mostly against a light source containing long wavelength light such as tungsten halogen lamp, and their practically applicable characteristics have been evaluated upon photocarriers generated as a result of absorption of long wavelength light by their photoconductive layer as a whole.
The known electrophotographic image-forming members having a photoconductive layer composed of an amorphous silicon carbide are mostly of the type that comprises an amorphous silicon carbide layer and a charge generating layer being disposed under or on said amorphous silicon carbide layer, wherein a charge (photocarrier) generated in said charge generating layer is injected into said amorphous silicon carbide layer to thereby form an electrostatic latent image. These known electrophotographic image-forming members have been usually considered as being practically usable as long as at least either electrons or holes in their amorphous silicon carbide layer have a sufficient carrier range.
Thus, it can be said that the known amorphous silicon carbide films have a practical applicability when used as the photoconductive layer of a photosensitive image-forming member for use in an ordinary-speed electrophotographic copying system or in an ordinary-speed printing system.
However, any of the known electrophotographic image-forming members having a constituent layer formed of a known amorphous silicon carbide film are not sufficient to satisfy all the requirements for an electrophotographic image-forming member for use in a high-speed electrophotographic copying system using a coherent light laser beam as the light source or in a high-speed printing system.
For example, for a known electrophotographic image-forming member having a photoconductive layer formed of a known amorphous silicon carbide film, when it is used in said high-speed electrophotographic copying system and the electrophotographic image-forming process including corona-charging operation and exposing operation is continuously repeated, there often occur pinholes thereon due to repeated corona charging operations at high speed to cause the formation of defective images. In this case, there also often appear ghosts on the resulting copied images.
Further, the electrophotographic image-forming process in the foregoing high-speed electrophotographic copying system is relatively complicated in order to repeatedly provide a high quality image at high speed. There is a problem for the foregoing known amorphous silicon carbide image-forming member when used in such complicated electrophotographic image-forming process in that dark decay is apt to occur because of repeated corona-charging operations at high speed.
Further in addition, in the foregoing electrophotographic image-forming process, corona-charging, image-exposure, development, image-transfer, and cleaning are continuously repeated at high speed. In that process pre-exposure is conducted to eliminate the residual potential resulted from the previous image-pattern prior to conducting said corona-charging. There is a problem for the foregoing known amorphous silicon carbide image-forming member in this that electrons and holes are apt to be trapped within its photoconductive layer respectively in a large quantity because of said pre-exposure. Those electrons and holes once trapped within the photoconductive layer are released at the time of corona-charging to cause a decrease in the initial surface electric potential, which leads to increase in a dark decay for the image-forming member. In this case, there is another problem in that those electrons and holes as trapped within the photoconductive layer are apt to recombine with electrons and holes generated at the time of image-exposure to cause a decrease in the photosensitivity of the image-forming member.
As for the known amorphous silicon carbide film, when it is formed by way of a conventional RF-PCVD process, there is a problem when the deposition rate is 80.ANG./sec. or more, in that the electric characteristics of the resulting amorphous silicon carbide film become significantly reduced.
Further in addition, in the case of the known electrophotographic image-forming member having a photoconductive layer formed of a known amorphous silicon carbide film and a surface layer laminated on said photoconductive layer, when it is used in the foregoing high-speed electrophotographic copying system, the charge retentivity is relatively satisfactory in comparison to a member not having any surface layer, but because the rotation cycle is short, the surface electric potential is gradually decreased as corona-charging is repeated to cause a phenomenon called "a decrease in the initial surface electric potential". Occurrence of this phenomenon is different in terms of degree between the part of the photoconductive layer which was irradiated with light and the remaining part which was not irradiated with light. This causes appearance of a significant ghost on an image obtained.
It is commonly recognized that an electrophotographic image-forming member can be provided with a charge injection inhibition layer in order to prevent charges from being injected into the photoconductive layer from the side of the substrate. However there is a problem for an electrophotographic image-forming member comprising a substrate and a light receiving layer comprising a charge injection inhibition layer and a photoconductive layer formed of a known amorphous silicon carbide film being laminated in this order on said substrate when used in the foregoing high-speed electrophotographic copying system in that pinholes are apt to occur on the image-forming member because the electrophotographic image-forming process is continuously repeated at high speed and the related conditions including charging condition eventually become severe.
Against the above background, high-speed electrophotographic copying systems gradually have come into wide use. There is an increased social demand for providing an inexpensive desirable electrophotographic image-forming member which can sufficiently satisfy the requirements for such high-speed copying systems and which can stably exhibit the desired functions as the electrophotographic image-forming member for said systems, by using an amorphous silicon carbide film and utilizing the various advantages thereof.